In the known devices of this kind, the pressure control valve of the tire should be open during inflation and deflation of the tire to the desired pressure and closed once the pressure in the supply conduit is of the order of 1 bar.
In practice, in order to avoid premature wearing of the rotating joints which lead from the pressure supply in the chassis to the tires, the pressure is normally relieved in the device by a purging system except during the relatively brief periods when the pressure in the tire is being modified.
In addition, these devices, attached to each wheel, should function under extreme conditions of temperature, shocks and vibration, and should remain sealed tight against sand, mud, and all kinds of liquids such as water, oils and naphthas.
To do this, it is known, as described in the French Certificate of Utility No. 82 11002, to make sealed devices without a purging system to communicate with the exterior, and possessing a chamber, called a respiration chamber, isolated from the inlet and outlet chambers by a flexible diaphragm. This chamber contains a spring serving to press the valve head against its seat to close the inlet channel. This valve head is provided with an anti-backflow device which allows the connection between the respiration chamber and the outlet channel to evacuate any excess pressure from the said chamber. However this system has the disadvantage that, in the case of a leak at the level of the diaphragm and because of the presence of the anti-backflow device, all the air can leak out of the tire via the inlet conduit from which the pressure has been relieved during normal driving.